Inner mold for molding cylinder

Abstract

An inner mold for molding a cylinder having a bore-forming core for forming a cylinder bore, and a shell core for forming a recess in the cylinder that can serve as, for instance, a scavenging passage. Holes are formed in the bore-forming core for allowing the shell core to fittingly engage with the bore-forming core, and the bottom surfaces of each of the holes are arcuately concaved.

I claim: 
     
       1. An inner mold for molding a cylinder having a bore-forming core for forming a cylinder bore, and a shell core disposed in fitting engagement with holes formed in said bore-forming core for forming a recess in the cylinder wall which may be used as a scavenging passage, the bottom surface of each of said holes of said bore-forming core being formed with an arcuately concaved surface. 
     
     
       2. An inner mold for molding a cylinder according to claim 1, wherein one circumferential end of each of said holes has a width greater than that of the other circumferential end.